Keying circuit for simultaneously switching a plurality of circuits

ABSTRACT

A plurality of circuits employed in an electronic musical instrument and having different time constants are simultaneously switched by a keying circuit according to the present invention which is so organized that the circuits to be switched are arranged in an increasing order of the time constants, a single switch is connected directly to a switching terminal of the firstly arranged circuit having the smallest time constant, and a plurality of diodes are disposed in such a manner that each diode is connected between adjacent switching terminals of the circuits and that the forward direction of the diodes is so arranged as to conduct at a closure of the above said single switch. When the circuits to be switched include one or several groups of circuits having similar time constants, each of such groups of the circuits are commonly connected to a switching terminal and arranged in an increasing order of the time constants to be organized into a keying circuit as described above.

United States Patent Hirose 1 May 16, 1972 [54] KEYING CIRCUIT FOR 3,037,413 6/1962 Markowitz ..84/D1G. s SIMULTANEOUSLY SWITCHING A 3,333,042 7/1967 Brombaugh ..84/D1G. 5 PLURALITY OF CIRCUITS Primary Examiner-Lewis H. Myers [72] Inventor: Yasunorl l-llrose, l-lamamatsu, Japan m Exam,-ner Stan|ey J. witkowski 731 Assignee: Nippon Gakki Seizo Kabushiki Kaisha,

l-lamamatsu-shi, Japan ABSTRACT [22] Filed: Apr. 17, 1970 Appl. No.: 29,506

A plurality of circuits employed in an electronic musical instrument and having different time constants are simultaneously switched by a keying circuit according to the present invcntion which is so organized that the circuits to be switched are arranged in an increasing order of the time constants, a single switch is connected directly to a switching terminal of the firstly arranged circuit having the smallest time constant, and a plurality of diodes are disposed in such a manner that each diode is connected between adjacent switching terminals of the circuits and that the forward direction of the diodes is so arranged as to conduct at a closure of the above said single switch. When the circuits to be switched include one or several groups of circuits having similar time constants, each of such groups of the circuits are commonly connected to a switching terminal and arranged in an increasing order of the time constants to be organized into a keying circuit as described above.

2 Claims, 4 Drawing Figures RIB 4 Patented May 16, 1972 3,663,737

2 Sheets-Sheet .I

F I G. I [PRIOR ART] BIAS SOURCE+ 6V Fl -2 [PRIORART] BIAS SOURCE 6V A INVENTOR kw: 7M

ATTORNEYS Patented May 16, 1972 2 Sheets-Sheet 2 OUT POWER 1 SOURCE H- NJ- f 5 i -IN I I IA-IVENTOR I (QVMQMJQQTW ATTORNEYS BACKGROUND OF THE INVENTION This invention relates generally to keying circuits, and more particularly to a type of keying circuits which can switch a plurality of circuits employed in an electronic musical instrument simultaneously.

It is known that, when a plurality of circuits, particularly keyers, to be switched each having a different time constant are switched simultaneously through the use of one switch, undesirable interference is generally caused between the time constants of the circuits. That is, the time constant of a circuit may be varied under the influence of other circuits commonly connected to the single switch so that the circuits will be simultaneously closed or opened by means of the single switch.

For this reason, whenever a plurality of circuits employed in an electronic musical instrument are to be switched simultaneously, these circuits are provided with individual switches or diodes so that the circuits-may be separated from each other. For instance, two keyers to be switched (keyed) simultaneously are provided with each of the individual switches K1 and K2 as indicated in FIG. 1, which will be described hereinafter in more detail, or are provided with individual diodes D1 and D2 as indicated in FIG. 2, which will also be described hereinafter, for isolating one circuit from the other.

However, with these organizations of the keying circuit, it is apparent that too many switches or diodes are required when the number of the circuits to be switched is increased. Furthermore, in the latter case where the diodes are employed, there are possibilities of drawbacks such as disturbance of the time constants of the circuits to be switched by deviations in the characteristics of the diodes, and decrease in the switching speed of a circuit having a smaller time constant due to the internal resistance (forward) of the diode connected in the circuit.

SUMMARY OF THE INVENTION Therefore, the primary object of the present invention is to provide an improved organization of a keying circuit wherein all of the above described drawbacks can be eliminated.

Another object of the present invention is to provide an improved organization of a keying circuit wherein the required number of the switches or diodes are substantially decreased.

Still another object of the present invention is to provide an improved organization of a keying circuit wherein the possibility of the time constants of the circuits to be switched being disturbed by the allowable production errors in the diodes is substantially eliminated.

An additional object of the present invention is to provide an improved organization of a keying circuit wherein the drawback of increase in the switching time of the circuit having a smaller time constant due to the internal resistance of the diode can be substantially eliminated.

These and other objects of the present invention can be achieved by an improved type of keying circuit for simultaneously switching a plurality of circuits employed in an electronic musical instrument and each having a different time constant, which is so composed that the plurality of circuits to be switched are arranged in an increasing order of the time constants, a single switch being directly connected to a switching terminal of one of the circuits having the smallest time constant, and a plurality of diodes each being connected between switching terminals of the circuits having different time constants so that all the diodes are conductive upon closing of the single switch.

In another aspect of the invention, whenever the circuits to be switched include one or more groups of circuits each group including circuits of substantially equal time constants, the keying circuit may be so arranged that a group of circuits having substantially equal time constants are connected commonly to a switching terminal, the above described arrangement of the circuits be followed substituting these groups of the circuits for the individual circuits.

The nature, principle, and utility of the present invention will be more clearly understood from the following detailed description with reference made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIGS. 1 and 2 are circuit diagrams showing two examples of conventional keying circuits both being applied for keying two sustain keyers included in an electronic musical instrument;

FIG. 3 is a circuit diagram showing an example of a keying circuit according to the present invention, which is employed for keying simultaneously a plurality of sustain keyers to be switched; and

FIG. 4 is a circuit diagram showing another example of a keying circuit according to the present invention.

DETAILED DESCRIPTION OF INVENTION Referring to FIG. 1 showing an example of a conventional keying circuit, to be employed for an explanation of r the present invention, there are indicated two sustain keyers, one including a transistor T1, resistors RlA through RID and a capacitor C1, wherein the build up time constant is mainly determined by ClRlA and the decay time constant mainly by ClRlD, and the other including a transistor T2, resistors R2A through R2D, and a capacitor C2, both of the circuits being connected to switches K1 and K2, wherein the build up time constant is mainly determined by C2R2A and the decay time constant is mainly determined by C2R2D.

With this arrangement of the keying circuit, it is apparent that the two circuits can be switched simultaneously without causing any interference between the time constants of these two circuits, which means that each circuit presents signal decay in accordance with its own time constant after the switches K1 and K2 are opened. Likewise, in FIG. 2 it is shown that the two sustain keyers similar to those shown in FIG. 1 are connected to two diodes D1 and D2, respectively, so that they may be connected thereafter to a single switch K. In this case the two circuits to be switched are isolated from each other by means of the diodes D1 and D2, and the above described interference between the time constants of the two circuits can be thereby prevented.

However, when the number of the circuits to be switched simultaneously is increased considerably, the type of keying circuit shown in FIG. 1 requires too many switches, which may result in non-simultaneous closures or openings upon operation of the key because of mechanical errors, and the other type of keying circuit as shown in FIG. 2 requires too many diodes.

Furthermore, in the keying circuit of the latter type, there are drawbacks such as the tendency of time constants of the circuits to be switched simultaneously to be varied by deviations in the characteristics of the diodes and the tendency of the smallest time constant of all the circuits to be switched to be increased by the internal resistance (forward) of the diode connected thereto.

These and other drawbacks of the conventional keying circuits can be overcome by an improved organization of a keying circuit as shown in FIG. 3. In the keying circuit shown in FIG. 3, the sustain keyer circuits to be switched simultaneously are of similar composition, for instance, of an emitter keyed amplifier, except that the switching time constants (built up and decay) thereof are different from each other. In the sustain keyer circuit 1, an input signal is applied to the base of a transistor T1, and an output signal is obtained across the collector resistor Rlc, which is thereafter taken out of an output terminal OUT. A resistor RlA, a capacitor C1, and another resistor RlD are connected to the emitter of the transistor T1, and a cut-off bias source +6V is connected to a terminal S. The simultaneous switching of the circuits I, 2,

and 3 are carried out by means of a single switch K which is directly connected to the emitter resistor RlA of the transistor T1.

Since all of the circuits 1, 2, and 3 are of similar construction arranged in an increasing order of the time constants, (this generally means that C1 C2 C3) the single switch K is connected to the emitter resistor RlA of the circuit 1 which has the smallest time constant. The mutual connection between the switching terminals (down sides of the emitter resistors) of the circuits 1, 2, and 3, that is, the mutual connections between the emitter resistors R and R and R and R are realized by connecting diodes D1 and D2 therebetween so that the forward directions of the diodes are so set as to conduct upon closure of the switch K, in this case directed from the circuit having a higher time constant to the circuit having a smaller time constant as the transistors are of an NPN type.

When the switch K is closed, all of the keyers l, 2 and 3 become conductive since the diodes are interposed in the forward direction. The build-up times are determined by the time constants of ClRlA, C2R2A and C3R3A, respectively. Next, when the switch K is opened, the circuit 1 which has the smallest decay time constant presents a short decay and becomes non-conductive first, and the rest of the circuits 2 and 3 become cut off successively and present a medium and a long decay in accordance with the magnitudes of the time constants. In this organization of the keying circuit, since the circuit 1 becomes non-conducting with its emitter potential raised to near +6V earlier than the circuit 2, and the circuit 2 becomes non-conducting earlier than the circuit 3, mutual interference between the circuits 1, 2, and 3 is prevented by the existence of the backward biased diodes D1 and D2. Every keyer circuit presents its own decay independently.

Furthermore, when the circuits to be switched include one or more groups of circuits having substantially equal time constants, each of such groups of the circuits may be connected commonly (without diodes) to a switching terminal andarranged in an increasing order of the time constants as described above. In this case, each of the diodes may be connected between adjacent switching terminals of the circuits or groups of circuits arranged in the above described order, whereby the number of diodes can be reduced substantially relative to the number of the circuits to be switched.

An example of such an organization of the keying circuit is shown in FIG. 4. In the drawing, the (sustain keyer) circuits to be switched 4, 5 and 6 have the same time constant, and the circuits 7 and 8 have the same time constant of another value, the former time constant being smaller than the latter. In this case, only one diode D3 is connected between the switching terminal of the first group of the circuits and the switching terminal of the second group of the circuits as indicated in the drawing, whereby the number of the diodes is substantially decreased. Of course, the keying operation of these circuits is attained by means of a switch K as in the case of FIG. 3, and the interference between the circuits having different time constants can be prevented by the existence of the diode D3.

According to the present invention, all of the circuits to be switched are rendered conductive or non-conductive simultaneously by means of a single switch with interference therebetween being substantially eliminated through the use of a minimum number of diodes. In addition, even though a circuit of a larger time constant is connected to the switch K through a larger number of diodes, the sum of internal forward resistances will not substantially influence the larger time constant. Therefore, no recognizable variation is caused in the time constants of the circuits, and the variation of the time constants due to production errors or deviations in the diodes can also be neglected.

I claim:

1. A keying circuit arrangement comprising:

a plurality of keyers, each including a transistor having a base electrode, a collector electrode and an emitter electrode, a signal input terminal which is connected to said base electrode and to which is supplied a signal to be switched, a signal output terminal which is connected to said collector electrode and from which is derived a switched signal, a switching terminal connected to said emitter electrode, and a capacitor and a resistor connected to said switching terminal and determining a decay time constant of each said keyer;

a single switch connected directly to said switching terminal of the keyer having the shortest time constant among said plurality of keyers; and

at least one diode connected between the switching terminals of said plurality of keyers, said keyers being arranged in the order of increasing time constants, the forward direction of said diode being the direction of a keying current for said keyers through said single switch upon closure thereof.

2. A keying circuit arrangement as defined in claim 1, wherein some of said plurality of keyers have the same time constant and are arranged together, a separate diode being connected only between the switching terminals of those circuits having time constants that differ with respect to one another. 

1. A keying circuit arrangement comprising: a plurality of keyers, each including a transistor having a base electrode, a collector electrode and an emitter electrode, a signal input terminal which is connected to said base electrode and to which is supplied a signal to be switched, a signal output terminal which is connected to said collector electrode and from which is derived a switched signal, a switching terminal connected to said emitter electrode, and a capacitor and a resistor connected to said switching terminal and determining a decay time constant of each said keyer; a single switch connected directly to said switching terminal of the keyer having the shortest time constant among said plurality of keyers; and at least one diode connected between the switching terminals of said plurality of keyers, said keyers being arranged in the order of increasing time constants, the forward direction of said diode being the direction of a keying current for said keyers through said single switch upon closure thereof.
 2. A keying circuit arrangement as defined in claim 1, wherein some of said plurality of keyers have the same time constant and are arranged together, a separate diode being connected only between the switching terminals of those circuits having time constants that differ with respect to one another. 